VTechWorks Repository :: Browsing by Author "Schuerch, Roger"

Browsing by Author "Schuerch, Roger"

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Apple orchards feed and contaminate bees during, but even more so after bloom
Steele, Taylor N. (Virginia Tech, 2021-11-16)
Honey bees, Apis mellifera Linn., provide vital economic and ecological services via pollination while concurrently facing multiple interconnected stressors impacting their health. Many crops like apples, peaches, and cherries that add diversity and nutrition to our diet are wholly or partially dependent upon the pollination services of insects. Orchard crops are self-incompatible and commonly regarded as crops reliant on the pollination services of insects, and while previous studies have focused on the impact of bees to orchard crops during bloom, fewer studies have examined the reciprocal relationship of the orchards on honey bees, particularly across the entire foraging season. Here we investigated the foraging dynamics of honey bees in an orchard crop environment in Northern Virginia, United States. We decoded, mapped, and analyzed 3,710 waggle dances, which communicate the location of a valuable resource in the environment, for two full foraging seasons (April-October, 2018-2019), and, concurrent to the dance filming, collected pollen from returning foragers. We found that bees forage locally the majority of the time (< 2 km) throughout the season, with some long-range distances occurring in May after bloom (both 2018 and 2019) and in fall (2019). The shortest communicated median distances (0.50 km and 0.53 km), indicating abundant food availability, occurred during September in both years, paralleling the bloom of an important late season resource, goldenrod (Solidago). We determined, through plotting and analyzing the communicated forage locations and from the collected pollen from returning foragers, that honey bees forage more within apple orchards after the bloom (29.4% and 28.5% foraging) compared to during bloom (18.6% and 21.4% foraging) on the understory of clover and plantain. This post bloom foraging also exposes honey bees to the highest concentration of pesticides across the entire foraging season (2322.89 ppb pesticides versus 181.8 during bloom, 569.84 in late summer, and 246.24 in fall). Therefore, post bloom apple orchards supply an abundance of forage, but also the highest risk of pesticide exposure, which may have important implications for management decisions of bees in orchards.
Biology and integrated pest management of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), in Southeastern cotton
Dorman, Seth Joseph (Virginia Tech, 2020-05-11)
The tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois), has been a devastating insect pest in cotton agroecosystems in mid-southern cotton for several decades. Similar to related Heteropteran insect pests, L. lineolaris uses piercing-sucking mouthparts to penetrate harvestable fruiting structures on the cotton plant (i.e., squares, flowers, small bolls) leading to significant reductions in lint yield when infestations are above economic injury levels. Economically damaging infestations of L. lineolaris have occurred in Virginia and North Carolina cotton since 2013. In response, cotton area sprayed with broad-spectrum insecticides for L. lineolaris has increased in these states. As such, this dissertation research sought to answer a variety of questions to address this issue including 1) mapping the spatiotemporal abundance of L. lineolaris across Virginia as well as creating models to predict landscape and climate factors increasing infestation risk, 2) using a systems approach to provide growers with cost-effective and sustainable integrated pest management (IPM) solutions including economic spray thresholds, 3) investigating the incidence and transmission of fungal pathogens by L. lineolaris increasing Fusarium hardlock disease, further impacting yield loss at harvest, and 4) conducting insecticide resistance monitoring of L. lineolaris across the Southeast including biochemical lab assays to determine possible mechanisms of insecticide resistance. These findings will help form compressive IPM and insect resistant management (IRM) plans to equip southeastern cotton growers with practical management tools as well as useful information on "high-risk" areas to invest management resources, increasing economic returns while minimizing environmental impacts of over-spraying foliar insecticides.
Biology of Chauliognathus spp. (Hentz) (Coleoptera: Cantharidae) in Virginia agroecosystems
Catron, Katlyn Amos (Virginia Tech, 2021-05-17)
Chauliognathus pensylvanicus (De Geer) and C. marginatus (Fabr.) are two of the most common species of cantharid beetles observed in agroecosystems in Virginia. Despite their widespread abundance and early recognition and description in the 1700s, little is known about their phenology and ecological role in agricultural systems. Immatures have been recorded feeding upon soft-bodied insects such as lepidopteran larvae, and adults frequently visit flowering plants, where they eat nectar and/or pollen. Beyond those observations, relatively little is known about these species, which are conspicuous elements on and around farms, though there is considerable potential for their use as pollinators and predators in a biological pest control context. I employed a phenological study to determine the period of C. marginatus activity in Southwestern Virginia, and found adults active on a variety of flowers from mid-May to late July. On these flowers, they spent a large percentage of their day mating or feeding, with significant differences in the percentage of beetles participating in behaviors based on time of day and beetle sex, but not based on month. The majority of C. marginatus observations occurred on narrowleaf mountain mint (Pycnanthemum tenuifolium Schrad.), poison hemlock (Conium maculatum L.), and wild bergamot (Monarda fistulosa L.). I also used a community science-based approach to evaluate the usage of host plants and flower colors by C. marginatus and C. pensylvanicus. Chauliognathus marginatus utilized white flowers more than expected based on their potential availability, while C. pensylvanicus utilized yellow flowers over all other flower colors and more than expected based on their potential availability. Communities of flowers available to and observed with C. marginatus and C. pensylvanicus differed significantly at the family and genus levels. Laboratory bioassays supported these conclusions regarding C. pensylvanicus color preference, but not C. marginatus color preference. Lastly, because of their susceptibility to nontarget chemical exposure in agroecosystems, I tested the efficacy of both organic and conventional vegetable insecticides against C. marginatus adults. The highest mortality was seen in the acetamiprid, flupyridifurone, sulfoxaflor, and imidacloprid treatments, which reached 97-100% mortality at two days after treatment. High mortality (60-97% two days after treatment) was also seen in the organic treatments containing azadirachtins, pyrethrins, and Chromobacterium subtsugae strain PRAA4-1T. Mortality in the Burkholderia spp. strain A396 and spinosad treatments was not significantly different from that of the controls, however, control mortality was relatively high in both assays.
Can Beef Be Bee-Friendly? Using Native Warm-Season Grasses and Wildflowers in Pastures to Conserve Bees
Wagner, Jennie Faith (Virginia Tech, 2020-05-29)
Over the past several decades, native and managed bee populations have decreased in the United States and worldwide. Although bee decline is attributable to several factors, habitat loss is the primary driver. Simultaneously, cattle producers in the eastern U.S. rely primarily on cool-season forages that peak in biomass production in late spring, leading to a lack of forage in the summer months and increasing the costs of cattle production. Seeding pastures with a mix of native warm-season grasses and native wildflowers could increase forage availability while also increasing available resources for bees. In this study, a mix of three native warm-season grasses (NWSGs) and 15 wildflower species was planted at the Virginia Tech Shenandoah Valley Agricultural Research and Extension Center (SVAREC). The objectives of this project were to document the establishment and species composition of NWSG + wildflower pasture mixtures, compare the attractiveness of wildflowers and weedy species to bees, and compare the bee community between NWSG + wildflower pastures and more typical cool-season grass pastures. The wildflowers in the NWSG + wildflower pastures dominated over grasses. All wildflower species that established were attractive to bees, as were some weedy species. The NWSG + wildflower treatments had the highest abundance of bees collected, with an average of 14.8 bees collected per pasture per sampling date in 2018, and an average of 12.4 bees collected per pasture per sampling date in 2019. These results indicate that with modification of establishment methods so that more grasses are present, this pasture system could be beneficial from both a cattle production and bee conservation standpoint.
Diapause biology, dispersal capabilities and insecticide use for Lygus lineolaris in Mid-Atlantic cotton systems
Schepis, John Philip (Virginia Tech, 2024-06-03)
Cotton (Gossypium hirsutum L.), is cultivated in the United States, primarily in regions characterized by long, hot summers to optimize plant growth. Virginia is the northernmost state where cotton is grown, with approximately 84,000 acres annually. The unique challenges of cultivating cotton in Virginia stems from its relatively short season due to its geographical location, lack of large contiguous acreage, and distinctive issues with pests. A significant pest of this region is the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), which emerged as a major threat to mid-Atlantic cotton during the late 2010s. L. lineolaris utilize a variety of wild and cultivated hosts to survive the winter months. The overwintering success and distribution of diapause survival L. lineolaris was measured on cover crops and weeds common in the Mid-Atlantic. Densities varied between weed and cultivated hosts, with L. lineolaris exhibiting increased survival in legumes compared to grains. Carbohydrate, lipid and protein levels were measured within diapausing and non-diapausing L. lineolaris specimens. Overwintering specimens usually had elevated level of carbohydrates and lipids, while containing decreased concentrations of protein. Nutrient quantification provided an effective tool in selecting for diapause status in L. lineolaris. Through the results from this study, an alternative method to dissection for determining diapause status in L. lineolaris has been identified. In the spring, movement of L. lineolaris throughout the landscape is highly dependent on host senesce. Flight analysis, behavioral assays and nutritional quantification assays on L. lineolaris populations from different weed hosts were performed to assess the flight capacity of specimens fed from different hosts. While weed hosts type provided populations with differing internal nutrient levels, sustained flight was not different between populations. When dispersal of L. lineolaris into cotton occurs, insecticide treatments following scouting are often necessary to prevent economic damage to the plant. Insecticide experiments were conducted aiming to assess the impact of different active ingredients on L. lineolaris, secondary pests, and natural enemy populations. Findings indicated that insecticides used to control L. lineolaris were successful at lowering pest populations and acephate was found to impact natural enemy populations. Plots applied with acephate experienced secondary pest outbreaks, highlighting the crucial role of natural enemies.
Drinking from the Magic Well: Studies on Honey Bee Foraging, Recruitment, and Sublethal Stress Responses using Waggle Dance Analysis
Ohlinger, Bradley David (Virginia Tech, 2023-06-05)
Anthropogenic landscape changes threaten our ecologically and economically critical honey bees by decreasing the availability of quality foraging resources. Importantly, waggle dance analysis provides a versatile and relatively cost-effective tool for investigating the obstacles that honey bees face, such as habitat loss, in our changing landscapes. While this emerging tool has improved our understanding of honey bee foraging in specific landscape contexts, additional research is needed to identify broad trends that span across landscapes. For this dissertation, I used waggle dance decoding and analysis to investigate honey bee foraging, and sublethal stress responses, across three ecologically distinct landscapes in Virginia. In Chapter 1, I introduce waggle dances as a model study system for investigating honey bee foraging and sublethal stress responses by summarizing modern methodological advances in its analysis and emerging research gaps. In Chapter 2, I tested the effects of sublethal imidacloprid exposure on honey bee foraging and recruitment using a semi-field feeder experiment. In doing so, I report that honey bees decreased their foraging, but not recruitment, to an imidacloprid-laced sucrose solution, compared to a control solution. Together, these effects could potentially harm honey bee health by increasing their exposure to pesticides and decreasing their food intake. In Chapter 3, I compared the foraging distances communicated by waggle dancing nectar and pollen foragers across landscapes to explore the economic forces driving foraging to these resources. I observed higher overall and monthly nectar foraging distances compared to pollen foraging distances. Such results suggest that nectar foraging cost dynamics are driven by supply, while pollen foraging cost dynamics are driven by demand. In Chapter 4, I used waggle dance decoding to map and quantify foraging to agricultural grasslands in a mixed-use landscape. In doing so, I demonstrate that honey bees recruit to agricultural grasslands throughout the season, but that this land type was not more attractive than the broader landscape after correcting for foraging distance, which is a relevant cost that flying bees must consider. Additionally, I qualitatively observe a foraging hot spot, representing high honey bee interest, over a highly heterogenous section of the landscape. The collective results of this chapter identify agricultural grasslands as a potential management target and support the importance of landscape heterogeneity to honey bees/pollinators. In Chapter 5, I used waggle dance decoding to investigate honey bee foraging spatial patterns in the context of optimal foraging theory. In particular, I explore whether co-localized honey bee colonies forage optimally by converging on the same resource patches, or by partitioning the landscape in to distinct foraging territories. Spatial analysis revealed that the colonies widely distributed their foraging at the landscape-scale, with dances from the same and different colonies being similarly distributed, while also establishing distinct, patch-scale, colony-specific, foraging aggregations. Together, these results suggest that the honey bee foraging system produces an emergent foraging pattern that may decrease both within- and among-colony foraging competition. Finally, in Chapter 6, I place my research findings in the context of historical and current trends in honey bee behavioral ecology. Overall, my dissertation improves our understanding of honey bee foraging ecology across landscape contexts using waggle dance analysis, while demonstrating its versatility and effectiveness as a tool for ecologists.
Ecology and Climate Tolerance of Emerging Tick Disease Vectors in Central Appalachia/Southwestern Virginia
Whitlow, Amanda Marie (Virginia Tech, 2021-06-29)
Little is known about the tick populations found within the central Appalachian/southwestern region of Virginia. The main focus of this research was to better assess local tick communities in the central Appalachian-Southwestern region of Virginia, which was addressed by determining species diversity, habitat associations, seasonal phenology, pathogen prevalence, and ecological factors that influences tick presence and abundance. A field study was conducted from June 2019 - November 2020 across 8 counties and 3 habitat types. Forested habitats exhibited greater tick species diversity than pasture and urban habitats. Each tick species was observed to be associated with particular habitats. The presence of B. burgdorferi sensu stricto (causative agent of Lyme disease), the human variant of A. phagocytophilum (causative agent of human granulocytic anaplasmosis), and Powassan virus (the causative agent of Powassan encephalitis) were detected in collected field specimens, suggesting a significant threat to public health. The detection of Powassan virus RNA in local Ixodes scapularis ticks is the first evidence of this viral pathogen within the region. The overwintering abilities of ticks, whose populations are expanding or becoming more invasive, including Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum, were examined through a combination of laboratory and field experiments. Amblyomma americanum and H. longicornis nymphal ticks had a lower supercooling temperature than adult ticks, suggesting their potential to overwinter better; A. maculatum nymphs had similar average supercooling temperatures as the other two species at nymphal stage. Via a field experiment, A. americanum, H. longicornis, and A. maculatum were subjected to natural elements of a Virginian winter in a two-factor design investigating elevation and potential insulation coverage. Elevation and insulation coverage were found to have no significant impact on the overwintering survival of H. longicornis and A. americanum. However, the life-stage of the tick was determined to be a significant factor that dictated the survival of ticks of these species. Overwintering survival of Amblyomma maculatum nymphs was influenced by insulation (proxied by leaf litter); which may be attributed to this tick's preference of drier climate. Low overwintering survival suggests that a tick may not be able to establish a permanent population within the area.
Environmental Fate of Ivermectin and its biological metabolites in Soils: Potential implications for the Environmental Impact of Ivermectin Mass Drug Administration for Malaria Control
Shija, Gerald Enos (Virginia Tech, 2023-02-02)
Despite significant vector control advancements in the past years, the current malaria trends suggest that new control strategies are urgently required. These new approaches should address the current frontline intervention challenges like increasing insecticide resistance in mosquitoes and residual transmission issues. Insecticide-treated livestock (ITL) is one of the novel potential strategies to overcome the above challenges. ITL involves treating livestock near humans with an insecticide like ivermectin (IVM) to kill zoophagic malaria vectors. However, ivermectin pharmacokinetics data suggests that most IVM-administered drugs remain intact, and more than 90 % of this drug is eliminated in feces. Biological metabolites: 3′′-O-demethylivermectin (3DI) and 24-hydroxymethyl ivermectin (24OHI) are also excreted in feces. Therefore, using manure from treated cattle as fertilizers contaminates the soil, ground, and surface water with IVM or its metabolites through leaching and hydraulic water flow affecting the soil and aquatic ecosystems. Contemplating the contamination impacts, these drugs' environmental fate and effects could be regarded before massive IVM applications. Many researchers have tried to address this subject in temperate regions compared to the tropics, where IVM is urgently needed. Regional discrepancies such as soil types and climate can independently and dependently determine the fate and impact of ivermectin. Our research investigates the environmental fate of IVM and its primary biological metabolites. Laboratory and field studies in Tanzania and Virginia were conducted to simulate the difference between tropical and temperate climates. Soil and soil-manure mixture spiked with IVM were layered into two 5 mm layers in columns exposed to natural sunlight. The remaining IVM and its primary metabolite were quantified using Liquid Chromatography with a tandem mass spectrometry detector (LC-MS/MS. These compounds degraded up to 1.5 times faster in Tanzania than in Virginia, depending on temperature, soil depths and type, organic matter, and soil moisture. When IVM is subcutaneously injected into cattle, drug residues and metabolites: 3DI and 24OHI are excreted in feces following a positive skewed Poisson distribution profile. IVM, 3DI, and 24OH were found to degrade rapidly when cattle pats when exposed to the field. Since we conducted our study in the Summer, no IVM or its metabolites leached into the soil beneath. The obtained half-lives suggest that ivermectin's massive drug administration has little to worry about, primarily when the dung from treated cattle is spread into the field in thin layers in the Summer before farm application.
Honey Bee (Apis Mellifera) Foraging Preferences are Negatively Correlated with Alfalfa Leafcutting Bee (Megachile Rotundata) Productivity in Virginian Landscapes
Campbell, Chad Dennis (Virginia Tech, 2023-06-21)
Honey bees (Apis mellifera) may serve as bioindicators of habitat quality for themselves and also other insect pollinators because we can observe, decode, map, and analyze the information encoded in the waggle dance communication behavior, which allows us to know where and when bees are collecting high quality forage. Previously we measured honey bee foraging dynamics for two years (2018-2019) by waggle dance decoding at three geographically distanced sites in Virginia (Blacksburg, Winchester, Suffolk), consisting of different dominant landcover types. Here we use those data on where and when honey bees were finding profitable resources throughout the season to predict the success of a non-Apis bee in these same landscapes. Alfalfa leafcutting bees (Megachile rotundata) are managed, polylectic, solitary, cavity-nesting bees that are widely naturalized in North America. We selected M. rotundata as a model organism to validate the honey bee foraging data because they share some characteristics with other cavity nesting wild bees, but they are a tractable study system because they are commercially reared and can be purchased for study. At each of the three sites, we installed 15 nest box stations, each stocked with nesting materials and 160 M. rotundata cocoons, at varying distances and directions from the original honey bee hive locations. Most importantly, nest box stations were distributed across a range of honey bee foraging propensities, calculated as the mean foraging probability determined from our honey bee waggle dance decoding data, within a 300m buffer around each nest box. We hypothesized that honey bee foraging probability would positively correlate with M. rotundata cocoon production and survival. For two years (2021-2022) from May-August, we monitored the nest boxes and also collected data on the relative abundance of floral resources at each of the 15 stations per site. At the end of each season, we collected nesting materials and counted both M. rotundata along with incidental (i.e., non-M. rotundata) wild bee cocoons. M. rotundata cocoon productivity varied by location (log-likelihood ratio test: χ2 = 311.0, df = 2, p < 0.001), with Winchester as the most productive location (mean cocoon count (95% CI): 26.2 (23.7 to 28.9)), followed by Blacksburg (20.4 (18.2 to 22.9)), and Suffolk (4.4 (3.5 to 5.5)). The abundance of clover, both red and white, had a significant positive effect on ALCB productivity (log-likelihood ratio test: χ2 = 778.36, < 0.001). On the other hand, the number of ALCB cocoons decreased significantly with the count of Trypoxylon wasp cocoons present in the nest boxes (log-likelihood ratio test: χ2 = 54.37, < 0.001). Most importantly, we found that there was an overall negative relationship between honey bee foraging probability and alfalfa leafcutting bee cocoon productivity ((log-likelihood ratio test: χ2 = 55.42, < 0.001), where areas of higher honey bee foraging probability were associated with lower levels of alfalfa leafcutting bee productivity. This surprising result is in the opposite direction to our original hypothesis that preferred honey bee foraging areas in the landscape, as indicated by decoded waggle dance data, would be positively correlated with alfalfa leafcutting bee productivity. These data demonstrate that while honey bees may indeed act as bioindicators to other insect pollinators, this indication will likely be species and context specific and may even specify the opposite direction.
The Impact of Ivermectin Treatment in Cattle on Dung Degradation and Fauna Abundance and Diversity in Tanzania
Ruhinda, Miriam Shani (Virginia Tech, 2023-06-08)
Ivermectin also called the wonder drug has been used over the years to control internal and external parasites in livestock. In humans it has been used for the control of several neglected tropical diseases. With regards to efforts to control malaria, mass drug administration (MDA) of ivermectin in humans and livestock has been considered as a potential tool. This is due to challenges in malaria preventive strategies such as insecticide resistance in mosquitoes, shift in their behaviors and residual transmission. Ivermectin reduces malaria transmission by targeting the mosquito nervous system resulting in their death. Ivermectin and its metabolites could have great impacts on the environment as well as human and health. In temperate settings, impacts of ivermectin in the environment were studied due to intense use of the drug in livestock. There is also a necessity to study effects of ivermectin in the tropics before MDA for malaria vector control. Despite its great potential, previous studies done recorded toxicity and sensitivity of the drug to most arthropods mainly dung organisms because ivermectin is released in dung at high concentrations for the case of livestock. With dung organism activity being affected the dung decomposition process is disrupted, cattle avoid these grazing areas leading to financial losses. In the tropics where there is a high number of malaria cases, there is no information on the impacts of the drug in the environment. We placed standardized dung pats from ivermectin-treated and control cattle to determine the effect of ivermectin on dung degradation and dung fauna in Tanzania. For the dung degradation study, at 15, 30 and 45 days post placement, we observed a total of 220 dung pats in the field. We measured termite colonization; wet weight of the entire pat; water content; dry weight of the 10 g subsamples and organic matter from subsamples and the whole pat. For the dung fauna study, we collected fresh dung 3, 10 and 29 days post treatment and put the pats out in the field to be colonized by insects before being transferred to emergence traps. We also did a semi field study where we collected dung pats 1,2,3 and 5 days post treatment to obtain larvae counts. We qualitatively assessed insect larvae activity in the field experiment and observed and counted larvae in the semi field study. We found that termites colonized pats from cattle treated with ivermectin more readily compared to controls (p < 0.001). Compared to control pats, the treated pats' wet weight decreased more slowly on day 15 (p < 0.001), day 30 (p < 0.001), and on day 45 (p = 0.037). Percent dry weight increased over time and similarly between the treatments as water content decreased. Organic matter of the 10g sub samples was similar between the treatments. Total organic matter in the whole pats showed significant differences on day 15 (p < 0.001), and day 30 (p = 0.003), but not on day 45 (p = 0.291). Qualitatively, we observed that pats from treated cattle had less insect larvae activity as compared to controls in the field study. In the semi field study, we counted less larvae in the pats from ivermectin-treated cattle than in the control pats (p < 0.001). Our results indicate that ivermectin and its residues affect dung degradation and dung fauna in tropical savanna settings, and the environmental safety may be at risk upon mass drug administration in livestock.
Interactions Between the Odorous House Ant (Tapinoma sessile) and RNA Viruses: a Multi-Faceted Approach
Hartle, Charly Taryn (Virginia Tech, 2024-05-28)
The odorous house ant, Tapinoma sessile, is a widespread, common pest in North American residential areas, yet the understanding of how viral pathogens shape its behavior, management, and interactions with other insects remains limited. Over the course of my thesis, I characterized four novel viruses in T. sessile using metatranscriptomic analysis, investigated their infectivity, and explored how colony social organization influences viral infection patterns. Inoculation experiments confirmed active infection in T. sessile colonies, suggesting trophallaxis as a route for horizontal transmission. These viruses were prevalent in urban populations with polygyne, unicolonial traits, indicating a potential association between colony social structure, colony location, and virus presence and diversity. Additionally, common honey bee viruses including Deformed Wing Virus and Kashmir Bee Virus were detected in T. sessile colonies, with higher prevalence near beehives, indicating a route for virus spillover between the species. Furthermore, the impact of viral infection on foraging behavior was assessed, revealing altered activity and diet preferences in infected colonies and highlighting the need for modified control strategies. Finally, I explored virus transmission between T. sessile and associated arthropods and found shared viruses and active replication in arthropods within ant nests, indicating a novel case of virus spillover between ants and myrmecophiles. These findings offer insights into viral pathogen interactions within ant colonies, the influence of social organization on infection dynamics, and the potential for pathogen transmission between ants and associated arthropods and offer a deeper understanding of an important native ant species that may shape future pest management strategies.
Portable, low-cost samplers for distributed sampling of atmospheric gases
Hurley, James; Caceres, Alejandra; McGlynn, Deborah; Tovillo, Mary; Pinar, Suzanne; Schuerch, Roger; Onufrieva, Ksenia; Isaacman-VanWertz, Gabriel (2023-10-13)
Volatile organic compounds (VOCs) contribute to air pollution both directly, as hazardous gases, and through their reactions with common atmospheric oxidants to produce ozone, particulate matter, and other hazardous air pollutants. There are enormous ranges of structures and reaction rates among VOCs, and consequently a need to accurately characterize the spatial and temporal distribution of individual identified compounds. Current VOC measurements are often made with complex, expensive instrumentation that provides high chemical detail, but is limited in its portability and requires high expense (e.g., mobile labs) for spatially resolved measurements. Alternatively, periodic collection of samples on cartridges is inexpensive but demands significant operator interaction that can limit possibilities for time-resolved measurements or distributed measurements across a spatial area. Thus, there is a need for simple, portable devices that can sample with limited operator presence to enable temporally and/or spatially resolved measurements. In this work, we describe new portable and programmable VOC samplers that enable simultaneous collection of samples across a spatially distributed network, validate their reproducibility, and demonstrate their utility. Validation experiments confirmed high precision between samplers as well as the ability of miniature ozone scrubbers to preserve reactive analytes collected on commercially available adsorbent gas sampling cartridges, supporting simultaneous field deployment across multiple locations. In indoor environments, 24-hour integrated samples demonstrate observable day-to-day variability, as well as variability across very short spatial scales (meters). The utility of the samplers was further demonstrated by locating outdoor point sources of analytes through the development of a new mapping approach that employs a group of the portable samplers and back projection techniques to assess a sampling area with higher resolution than stationary sampling. As with all gas sampling, the limits of detection depend on sampling times and the properties of sorbent and analyte. Limit of detection of the analytical system used in this work is on the order of nanograms, corresponding to mixing ratios of 1-10 pptv after one hour of sampling at the programmable flow rate of 50-250 sccm enabled by the developed system. The portable VOC samplers described and validated here provide a simple, low-cost sampling solution for spatially and/or temporally variable measurements of any organic gases that are collectable on currently available sampling media.
Quantifying macroinvertebrate structural and functional response to stream acidification and subsequent recovery in Shenandoah National Park
McIntyre, Kelly Christine (Virginia Tech, 2021-07-14)
Acid rain alters freshwater pH and ion composition, preventing organisms from performing essential bodily functions causing mortality. Macroinvertebrate communities in acidified streams are characterized by species loss in response to physiological stress and altered food quality resulting from the degradation of microbial (e.g., fungi on leaves) communities. Although freshwater acidification in the U.S. is lessening following reduced industrial emissions, little is known about macroinvertebrate recovery. Often, biotic recovery is assessed by looking at changes to what taxa and how many individuals are present in the community (e.g., richness, density). While providing a metric for change, changes in "who" is there (i.e., richness) doesn't necessarily tell us changes in "what" they are doing (i.e., function). The relationship between diversity and function requires linking a "who" to their "what" with direct measurements or as indicated by their traits. Traits are attributes of an organism that aggregate biological, morphological, and behavioral information and may relate to their success in a particular environment. For example, taxa that cannot survive with stream drying (not desiccation resistant) may only be found in streams with permanent water. Trait-based taxonomic metrics could bridge "who" and "what" and expand the impact of stream recovery assessments. My objective was to assess trends over time in water chemistry and macroinvertebrate taxonomic and trait richness and density following reduced industrial emissions. To do so, I studied two long-term data sets from Shenandoah National Park to assess trends in water chemistry and macroinvertebrate taxa and trait composition over a 30-year period to identify taxa and traits that are sensitive to acidification. I also measured how much biomass macroinvertebrates produced in a year (i.e., secondary production) in two streams (1 acidified; 1 not acidified) to determine taxa and traits that are functionally sensitive to acidification. I used these structural and functional measures of sensitivity to determine if changes in trait richness or density predict changes in the function of that trait (e.g., secondary production). Changes over time show that streams have some recovery from acid rain with increasing stream pH and a greater number of taxa and traits present in the community. Changes in taxa were greater than changes in traits over time. While this result was expected as multiple taxa make up each trait category, it may also suggest minimal or delayed functional recovery over time. Still, macroinvertebrate secondary production indicated that function did differ with differences in acidification. Therefore, observed small changes in traits over time mirror prior studies that found other variables, such as competition for food or space, delay or inhibit macroinvertebrates from returning to the recovering streams. Additionally, there were similarities between traits changing over time and the secondary production of traits that differed between more and less acidified streams. Taxa characterized by long life spans and large body size (e.g., semivoltine, long adult life, slow seasonal development) appeared to be the most sensitive to changes in acidification. These findings suggest that some compositional attributes, like taxonomic or trait richness, may predict functional changes measured as secondary production while others, such as density, do not.
Row crop environments provide an all-you-can-eat buffet and pesticide exposure to foraging honey bees
Silliman, Mary Rachel (Virginia Tech, 2021-06-03)
The western honey bee, Apis mellifera, provide invaluable economic and ecological services while simultaneously facing stressors that may compromise their health. For example, agricultural landscapes, such as a row crop system, are necessary for our food production, but they may cause poor nutrition in bees from a lack of available nectar and pollen. Row crops are largely wind or self-pollinated, and while previous studies have focused on the impact of bees to row crops, fewer studies have examined the reciprocal relationship of the row crops on honey bees. Here we investigated the foraging dynamics of honey bees in a row crop environment. We decoded, mapped, and analyzed 3460 waggle dances, which communicate the location of where bees collected food, for two full foraging seasons (April – October, 2018-2019), and concurrently collected pollen from returning foragers. We found that bees foraged mostly locally (< 2 km) throughout the season. The shortest communicated median distances (0.48 and 0.32 km), indicating abundant food availability, occurred in July in both years, which was when our row crops were in full bloom. We determined, by plotting and analyzing the communicated locations, that most mid-summer foraging was in row crops, with at least 40% of honey bee recruitment dances indicating either cotton or soybean fields. Bees also largely foraged for nectar when visiting row crop fields, only returning to the hive with Glycine spp. pollen, and foraging on nearby trees and weeds for pollen. Foragers were exposed to thirty-five different pesticides throughout the foraging season, based on pesticide residues in collected pollen. Overall, row crop fields are contributing a surprising majority of mid-summer forage to honey bee hives and suggests that similar agricultural landscapes may also provide abundant, mid-summer forage opportunities for honey bees, however, at the risk of pesticide exposure.
Row crop fields provide mid-summer forage for honey bees
Silliman, Mary R.; Schuerch, Roger; Malone, Sean; Taylor, Sally V.; Couvillon, Margaret J. (Wiley, 2022-07)
Honey bees provide invaluable economic and ecological services while simultaneously facing stressors that may compromise their health. For example, agricultural landscapes, such as a row crop system, are necessary for our food production, but they may cause poor nutrition in bees from a lack of available nectar and pollen. Here, we investigated the foraging dynamics of honey bees in a row crop environment. We decoded, mapped, and analyzed 3459 waggle dances, which communicate the location of where bees collected food, for two full foraging seasons (April-October, 2018-2019). We found that bees recruited nestmates mostly locally (<2 km) throughout the season. The shortest communicated median distances (0.474 and 0.310 km), indicating abundant food availability, occurred in July in both years, which was when our row crops were in full bloom. We determined, by plotting and analyzing the communicated locations, that almost half of the mid-summer recruitment was to row crops, with 37% (2018) and 50% (2019) of honey bee dances indicating these fields. Peanut was the most attractive in July, followed by corn and cotton but not soybean. Overall, row crop fields are indicated by a surprisingly large proportion of recruitment dances, suggesting that similar agricultural landscapes may also provide mid-summer foraging opportunities for honey bees.
Spread of Red Imported Fire Ant, Solenopsis invicta, in Virginia and effects of sub-lethal exposure to agrochemicals on its behavior
Malone, Morgan Le Fae (Virginia Tech, 2022-01-14)
Solenopsis invicta is an invasive ant that has caused detrimental impacts to ecosystems and economies in the Southeastern United States, recently including Virginia. In this study, we explored the invasion ecology of S. invicta through two main objectives. First, we established a comprehensive distribution map of S. invicta in Virginia through multiple survey techniques. We then compared our findings with published models quantifying the potential spread of S. invicta and created our own species distribution model. In 2020-2021, S. invicta occurrences were found in 7 counties beyond the current Quarantine and our data show that S. invicta has spread further than predicted. Our own species distribution model suggests that the distribution area for S. invicta is likely to increase under the projected climate change. This study provides insights into the range expansion of S. invicta at the border of its suitable habitat and allow for improvements to models of its spread under these conditions. Additionally, it provides useful information to inform county extension agents to know where they are to expect new infestations of S. invicta. Second, we investigated the impacts of pesticide residue on the behavior of S. invicta through neonicotinoid exposure. We found detectable levels of neonicotinoids in the soil of the ant mounds as well as in the ants themselves. In addition, we investigated the effects of dietary exposure to imidacloprid on foraging behavior in a laboratory setting. We found that unexposed colonies were able to locate the food source more quickly during the second trial while exposed ants were unable to improve their performance. We also found that more exposed ant workers were unable to successfully navigate the maze as compared to unexposed workers. Our results suggest impaired learning of maze tasks and impaired navigational skills in neonicotinoid-exposed ants.
A Study of Neonicotinoid Seed Treatments in Bt Maize: Insect Resistance Management, Efficacy, and Environmental Fate
Bekelja, Kyle (Virginia Tech, 2022-06-10)
Roughly 79-100% of maize in the United States (US) is treated with a neonicotinoid seed treatment (NST), and transgenic (GMO) maize, Zea mays L. (Poaceae), that produces insecticidal toxins by way of genes derived from Bacillus thuringiensis (Bt), occupies more than 75% of maize acreage. Among a variety of secondary pests targeted by NSTs, the primary soil-dwelling pest targeted by Bt maize is the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). Transgenic Bt technology has dramatically reduced insecticide use for WCR, and insect resistance poses the greatest threat to its utility. To delay resistance to Bt traits, in 2010 the US Environmental Protection Agency (EPA) approved a "refuge-in-a-bag" (RIB) insect resistance management (IRM) strategy, where 5% of seeds do not express Bt toxins (i.e., "refuge" maize). The RIB strategy is intended to preserve Bt trait effectiveness if mating between 'resistant' insects from Bt plants and 'susceptible' insects from refuge plants occurs at a high enough frequency. Investigations into the effectiveness of RIB for WCR have shown that beetles emerged from Bt plants tend to vastly outnumber beetles emerged from refuge plants, which contributes to low rates of mixed mating. Large proportions of Bt beetles is one of several factors that contributes to resistance development, and resistance to all currently-available WCR-Bt traits has been documented. I conducted field experiments in two regions (Indiana and Virginia) comparing refuge beetle proportions in NST-treated (NST+) and NST-untreated (NST-) 5% RIB maize, to determine whether NSTs may be limiting refuge beetle emergence. To assess advantages of combining use of Bt and NSTs, I compared stand, root injury rating, and yield between NST+, NST-, Bt and non-Bt maize in both states. I also measured neonicotinoid residues in soil, water, and stream sediment within and surrounding fields of maize, to study the off-site movement and soil residence time of these compounds. I found that 5% seed blends did not produce large populations of refuge beetles in any site-year, and that NSTs showed inconsistent effects on refuge beetle populations. Treatment comparisons showed inconsistent benefits of NSTs when combined with Bt traits. I detected neonicotinoid residues in soil matrices throughout the growing season (range: 0 – 417.42 ppb), including prior to planting, suggesting year-round presence of these compounds. My results suggest that, while the effects of NSTs on Bt IRM may be inconsistent, the benefits of universally applying NSTs to Bt maize for soil pests may not be worth the ecological costs of doing so in all cases.
Thresholds and Critical Growth Stages for Brown Stink Bug, Euschistus servus (Say), Management in Field Corn, Zea mays
Bryant, Timothy Basil (Virginia Tech, 2020-03-20)
The brown stink bug, Euchistus servus (Say), is a polyphagous pest of multiple cultivated hosts in Virginia. It recently emerged as a potentially devastating pest of maize, Zea mays L. (Poaceae), in eastern Virginia where small grain (e.g., wheat, rye) production is common. In order to develop an integrated pest management (IPM) plan, research is needed to determine if brown stink bug feeding causes economic damage in maize at different growth stages and levels of infestations. Experiments were conducted in 2018 and 2019 to determine: 1) effectiveness of seed applied and in-furrow chemical control methods, 2) infestation levels in seedling and reproductive growth stages that cause economic damage, and 3) the effect, if any, of E. servus feeding on grain quality and mycotoxin contamination. Results of these experiments demonstrated that infestation levels (i.e., number of bugs divided by number of plants) of 11% and 15% in seedling and late vegetative maize, respectively, can cause measurable yield reduction at harvest. Seedling damage from E. servus is significantly mitigated by neonicotinoid seed treatments which are applied to nearly all commercial maize seed. Further, experiments indicated that maize quality can be affected by E. servus feeding in late reproductive stages of development. Results of these experiments will help to inform Virginia maize producers of the need to manage E. servus throughout the growing season.
Waggle Dance Your Own Way: Individuality, Network Structure, and an Herbicide Stressor in Recruitment, Foraging, and Neurobiology in the Honey Bee (Apis mellifera L.)
McHenry, Laura Covington (Virginia Tech, 2024-10-22)
The waggle dance of the honey bee (Apis mellifera L.) is perhaps the most celebrated animal communication behavior. With a waggle dance, a forager bee who has discovered a profitable resource on the landscape, usually floral nectar or pollen, can inform her nestmates of its location and recruit them to exploit it by communicating both a distance and a direction. Since Karl von Frisch described the waggle dance in 1942, scientific exploration of the dance has exploded into the realms of its structure, function, role in the regulation of collective foraging in the context of the hive as a super-organism, and even its utility as a study system for understanding sublethal behavioral effects of pesticide exposure. This dissertation presents three novel studies of the waggle dance. In the first, we asked whether consistent inter-bee differences (i.e., individuality) in a waggle dance distance - duration calibrations could affect communication success. In the second, we characterized the networks of recruitment arising from waggle dance communications and explored the role of the aforementioned individuality in network formation. In the third, we tested whether sublethal exposure to glyphosate (GLY), the most-applied herbicide in the world, could affect foraging, recruitment, or the levels and balance of biogenic amines in the bee brain. In each of these experiments, we housed bees in clear-walled observation colonies and trained cohorts of bees to visit artificial feeders to record both foraging and recruitment data. In our first experiment, we found that individuality in waggle dance behavior does shape communication outcomes, indicating that individual-level behavioral differences should not be discounted as factors at work in eusocial insect societies. In the second, we present the first network density and dance burstiness data from in vivo bee networks, revealing that recruitment networks are sparse, and waggle dancers are partitioned into bursty and non-bursty behavioral types. In the third, we show that not only can sublethal GLY exposure reduce foraging, but it can also produce significant correlations between levels of the important insect neurotransmitter octopamine and its two biosynthetic precursors, tyramine and tyrosine, where levels in control bees were unrelated. The results of this dissertation research, while distinct by experiment, together emphasize the continuing usefulness and tractability of the honey bee colony as a system in which to study the role of individuality in animal communication and to better understand the threat posed by non-insecticidal pesticide chemistries to the planet's most economically impactful pollinator.

Browsing by Author "Schuerch, Roger"

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